Fluid expansion refrigeration method and apparatus



Sept. 29, 1959 H. o. MCMAHON ErAL 2,906,101

FLUID EXPANSION REFRIGERATION METHOD AND APPARATUS Filed Nov. 14, 1957 2 Sheets-Sheet 1 0rd vW l'aWz SUPPL Y Sept. 29, 1959 H. o, McMAHON ET AL FLUID EXPANSION REFRIGERATION METHOD AND APPARATUS Filed NOV. 14, 1957 2 Sheets-Sheet 2 flare/war; Harvard 0. Mild/207a (/Zzi a Unite States Patent FLUID EXPANSION REFRIGERATION METHOD AND APPARATUS Howard 0. McMahon and William E. Gilford, Lexington, Mass, assignors to Arthur D. Little, Inc., Cambridge, Mass, a corporation of Massachusetts Application November 14, 1957, Serial No. 696,506

Claims. (Cl. 62-6) This invention relates to refrigeration methods and apparatus for the production of low temperatures and liquefied gases at low temperatures.

One well known form of refrigeration apparatus comprises a cylinder having relatively Warm and cold ends interconnected through a cooler and a regenerator, 'respectively for removing heat of compression and for storing heat. Movement of a piston-like displacer within the cylinder causes the working fluid to flow in either of two directions through the regenerator. A separate piston, also within the cylinder, alternately compresses and expands the volume of fluid in the chambers in coordination with the displacer. The displacer and piston are separately driven, usually by cams, such that the fluid volume is compressed after the displacer has moved it to the warm end; the displacer then moves the fluid to the cold end through the cooler which removes heat of compression and through the regenerator which further cools the fluid; and the piston then allows the cooled fluid to expand in volume and thereby further cool itself and the surrounding cylinder. The refrigeration so produced may be extracted by heat exchange with the cooled cylinder or fluid.

While such engines are practical for producing moderately low temperatures in the order of 100 K., they are not Well suited for producing temperatures near absolute zero. The compression piston must be very closely fitted with sealing rings to prevent loss of the working fluid. The close fit requires lubrication which tends to contaminate the fluid. Moreover, friction losses occur and careful maintenance of the seal is required. Appreciable heat loss occurs through the rod used to drive the compression piston, and other frictional loss occurs in the complicated cam drive needed to coordinate the piston and displacer.

Previously it has been proposed to achieve lower tem perature refrigeration by operating several engines at a series of temperature levels so that the cooled fluid from one engine provides a low temperature for the starting point of a succeeding engine. Such systems have employed the tightly fitted compression pistons and cylinders, separate drives and complicated mechanical drive connections between compression pistons and displacers. In colder stages the piston seals must act at relatively high and low temperatures. Heat loss is higher in the low temperature stages owing to the external mechanical con: nection to the piston of each of the stages. Generally a multiple engine system multiplies the disadvantages of single stage engines, and introduces additional disadvantages.

One object of the present invention is to provide a novel method of fluid refrigeration which eliminates the need for close cooperation between the cyclic fluid compression and expansion of prior methods and which more efficiently utilizes expansion cooling of a refrigeration fluid.

According to the invention a fluid refrigeration method comprises continuously compressing a fluid, removing heat of compression and storing the compressed fluid, connect- H shown partly in section.

ing the stored fluid with an enclosed spaced thereby to sup ply compressed fluid thereto, partially cooling the fluid during supply, allowing expansion of the volume of cooled fluid in said space further to cool the fluid, and exhausting the further cooled volume of fluid from said space extracting refrigeration from the fluid and warming the fluid during exhaust.

Further objects of the invention are to provide novel apparatus for carrying out a refrigeration process which avoids operation of valves at low temperatures, which eliminates complicated mechanism for coordinating pistons and displacers, and which is adapted for multi-stage refrigeration while avoiding the use of pressure seals at low temperatures.

Further according to the invention, refrigeration apparatus comprises an enclosure, movable means forming with the enclosure an expansible chamber, valve means external of the enclosure for admitting compressed fluid to and releasing fluid from said chamber, and a conduit including thermal storage means between said chamber and said valve means thermally isolating said valve means from said chamber, said fluid undergoing expansion and cooling in said chamber, and said movable means causing exhaust of said cooled gas through said conduit. Such apparatus is easily adapted to multi-stage refrigeration when characterized by movable means such as a piston which includes a plurality of sections respectively forming with the enclosure a plurality of concomitantly expansible chambers, with at least one thermal storage means connected between said respective chambers.

For the purpose of illustration typical embodiments of the invention are shown in the accompanying drawings in which Figs. 1, 2, 3a, 3b and 4 are schematic views illustrating the operation of refrigeration apparatus; and

Fig. 5 is a diagrammatic view of a refrigeration system,

In Figs. 1 to 4 is illustrated schematically the operating cycle of the present refrigeration process. From any convenient low pressure source LP a refrigerating fluid, such as helium, is continuously compressed in a compressor C storage device 30 such as a regenerator.

In the basic cycle of operation, the first step, illustrated in Fig. 1, is the supply of the continuously compressed and. cooled fluid to the chamber *9, (see Fig. 2) now substantially filled by the piston 2. During supply the fluid is partially cooled by the regenerator 30 whose temperature is reduced as will hereafter be explained. The compressed fluid is then taken into the chamber (Fig. 2).- The supply of fluid is then discontinued by closing valve- V1, and the partially cooled fluid expands and cools itself and the chamber 9 in a well-known manner-during further movement of the piston (Fig. 3a) mechanical energy being expended in such movement of the piston;

The original high pressuredrops and any remaining pr'es sure differential between the fluid and the low pressure source is then relieved asby opening valve V2 (Fig. 3b). If any pressure is released, expanding fluid will still further. cool. The cooled fluid is then exhausted from the charn-' her by downward movement of the piston 2 (Fig. A), and during exhaust the fluid cools the regenerator 30 and in turn is warmed by the regenerator to 'roomor other reference temperature. The warmed fluid is then compressed and the cycle repeated.

The above cycle is particularly well adapted for multistage cooling in the apparatus shown in Fig. 5. As 'shown in Fig. 5 multi-stage refrigeration apparatus coniprises a cylinder 1 in which are fitted piston sections 2, 3 and 4. The piston sections are connected mechanically by linear springs 7 and 8, and a spring 6 is disposed between piston section 2 and the cylinder end wall 1a so as to divide the cylinder into three chambers 9, 1t} and 11.

A piston rod '12, driven through a connecting pin 14 by a flywheel 13, reciprocates the uppermost piston section 4 from a down position, through the position shown, to an up position. Sealing rings 5, and if necessary, oil lubrication on the periphery of section 4, seal the chamber 11.

When the flywheel pin 14 coupled to the rod 12 is in its lowest position I, the top piston section 4 is in a position in which it abuts the intermediate cylinder 3, filling the intermediate space 11. The connecting springs 8 and 7 respectively hold the lower pistons 3 and 2 downwardly against the spring 6, so that adjacent piston sections abut each other and the lower piston 2 abuts the end wall 1a of the cylinder. Thus in this position the chambers 9, and 11 are filled by the piston sections. To achieve optimum evacuation of fluid from the chambers, the springs 6, 7 and 8 are formed with a rectangular cross-section, and when fully compressed fill annular recesses 16 in opposed piston faces and the cylinder end wall 5.

From the lower position I the respective piston sections are driven in an expansion stroke through position II shown in Fig. 5 to a fully expanded position III, in which the connecting pin 14 and the piston sections are in their uppermost position, and the chambers 9 to 10 are greatest in volume. Thereafter the flywheel 13 drives the pistons through a partially compressed position IV to the fully compressed position I previously described.

The relative lengths of the springs between the piston faces, or their stiffness, are selected such that the three chambers are progressively larger in volume in the order 9, 10 and 11. As will be more fully explained, a temperature diflerential exists between the chambers, chamber 9 being the coldest, chamber 10 being warmer and chamber 11 the warmest. With substantially the same pressure in all of the chambers, their relative volumes will depend on the lowest temperatures at which it is desired to operate the engine. It may be desirable to open the lower chamber 9 in advance of opening chambers 10 and 11, in which case the lowest spring 6 would be selected to cause sections 3 and 4 to follow section 2 during the early part of its stroke. By different selections of spring rates, another chamber may be caused to open first, or all three chambers may be caused to open simultaneously.

Communicating with the chambers 9, 10 and 11 respectively are ports 17, 18 and 19 which include narrow, shallow channels in the inner cylinder wall. Connecting the ports are conduits 21, 22 and 23 which pass through thermal storage means 24 and 25 such as regenerators. Thermal transfer means 20 such as a heat exchanger having a. secondary input 27 and output 28 for a refrigerating medium is connected between the chamber 9 and regenerator 24. From conduit 23 a supply conduit 29 is connected through a regenerator 30 to valves V1 and V2. It will be understood that, although omitted for the purpose of clearer illustration, insulation is provided around the cylinder 1, the regenerators 24, 25 and 30 and the heat exchanger 20.

Valve V2 is connected to a low pressure ballast tank LP which is exhausted by a compressor C. The compressor C pumps a refrigeration fluid through a water cooled heat exchanger A, for example, and thence through a cleaning device B for removing oil vapor, to a high pres- 4 sure ballast tank HP. Valve V1 when open supplies compressed fluid from the high pressure ballast HP to the supply conduit 29. A flask F supplies fluid to the system through a check valve as needed.

By way of example, the opening and closing of valves V1 and V2 is accomplished by earns 31 and 32, respectively operating through follower rods 33 and 34 pivotally connected to valve levers 35 and 36. The valve cams are driven through a connection 37 in synchronism with the flywheel 13. Of course, one valve performing the function of the two valves shown may be substituted for the two valves shown.

The cycle of operation of the apparatus of Fig. 5 is as follows:

In flywheel position I the chambers 9 to 11 are substantially filled by the piston sections and exhausted of fluid. Both valves V1 and V2 are closed. Clockwise rotation of the flywheel toward position II opens valve V1 admitting fluid under pressure and at reference temperature, 300 K. for example, to the supply conduit 29. Concomitantly, that is, during overlapping periods, the piston sections begin an expansion stroke expanding the inter-piston chambers. Expansion of the chambers draws fluid through the thermal storage means 30, 25 and 24 to the chambers. Because the upper storage means 30 acts as a precooler for the middle storage means 25, and the middle a precooler for the lower means 24, the several storage means are at progressively lower temperatures descending in the order 30, 25 and 24, so that fluid entering chamber 9 will be colder than that entering chamber 10, which in turn is colder than that entering chamber 11. Valve V1 remaining open, the pressure remains high despite cooling of the fluid during intake.

At position H, valve V1 is closed, and the continuing expansion stroke isentropically expands the fluid in all three chambers. Since the fluid is at high pressure, as described above, it moves the piston upward in the manner described with reference to Fig. 3a, and thereby delivers mechanical work externally of the cylinder 1, which work is delivered to the flywheel 13 and absorbed by a brake 15 (Fig. 5). In the process of expansion the fluid in each chamber is cooled, according to well-known principles, below its starting temperature just prior to expansion. Since the several starting temperatures are progressively lower in chambers 11, 10 and 9 respectively, their final temperatures will be progressively lower, that in chamber 9 being the lowest. The walls of the chambers will simultaneously be cooled by the fluid toward the same temperatures.

At position III valve V2 is opened, connecting the chambers with the low pressure ballast LP. The fluid in the chambers may then further expand and cool during exhaust through the thermal transfer means 24, 25 and 30, but preferably the latter part of the expansion stroke of the piston sections reduces the fluid pressure to that of the low pressure ballast LP.

From positions III to I, valve V2 remains open and V1 closed, and during the accompanying compression stroke the piston sections fill the chambers and exhaust the cooled fluid through the several storage means. Since the low pressure ballast LP may be at the same pressure as the expanded fluid in the chambers, no external work need be expended on the flywheel during the herein-called compression stroke.

During exhaust the fluid in chamber 9, having started the cycle at a lower temperature than that in chamber 10, and having been further cooled by expansion, will cool the lower thermal storage means 24 below the temperature of storage means 25. Likewise storage means 25 will be cooler than means 30. In cooling the thermal storage means the fluid from the various chambers is progressively warmed until, after passing through the upper regenerator 30 it is returned substantially to room or reference temperature before reaching the valves V1 to the walls of the various chambers. However, for very low temperature purposes, only refrigeration from the lowest chamber 9 will be extracted, the upper chambers 10 and 11 serving progressively to cool the regenerators 25 and 30 which assist in providing the low starting temperature in chamber 9.

From the foregoing it is seen that with a single piston rod and cylinder the piston sections perform the function of several refrigeration stages. The seals for the upper piston section operate somewhat above the temperature of the warmest chamber 11, and because there is little pressure differential between the chambers the lower piston sections need not be tightly fitted or oiled, thus minimizing contamination of the cooling fluid. Leakage from the low temperature chambers 9 and is minimized by elimination of direct external mechanical connection to the inner cylinder sections from the normal temperature environment. nections also permits filling of the chamber with minimum clearance between piston sections on the full compression stroke. On the other hand, the valves operate at near to normal temperature beyond the relatively high temperature upper transfer means 30.

It should be understood that, while the conduits and thermal storage means are shown connected externally of the cylinder, other forms of conduits and storage means may be employed. And, although low and high pressure ballasts connected to the chambers by separate valve means are shown, various other fluid supplies may be used.

Thus the present disclosure is for illustration only and the invention includes all modifications and equivalents falling within the scope of the appended claims.

We claim:

1. A multistage, fluid refrigeration system comprising a low pressure ballast, a compressor, a thermal exchange cooler and a high pressure ballast connected in series to provide in said high pressure ballast a continuous supply of compressed fluid at approximately ambient reference temperature, a cylinder, a plurality of spring coupled piston sections reciprocable in said cylinder and forming therewith a plurality of spaced chambers, a single piston drive means extending externally of the cylinder and connected to one piston section for causing said sections concomitantly to expand and compress said chambers, valve means external of the cylinder for supplying compressed fluid to and releasing fluid from said chambers, conduit means connecting said valve means to one of said chambers at one end of the cylinder including thermal storage means thermally isolating said valve means from said one end, said chambers decreasing in relative volume in a direction away from said valve means, additional conduit means, including thermal storage means, between each of said chambers, and means for coordinating actuation of said drive means and valve means such that said valve means supplies compressed fluid from said high pressure ballast to said chamber through said thermal storage, said chambers are expanded by said piston sections, fluid is caused to expand and cool in said chambers, and said piston sections cause exhaust of said cooled fluid through said storage means after said valve means connects said chambers with said low pressure ballast, so that said storage means are cooled Elimination of external conduring'exhanst and the cooled fluid flowing durin 'exhaust is warmed by the storage means before reaching the valve means, and the fluid flowing during supply is cooled by the storage means, the fluid flowing into the chamber most remote from the valve means being cooled by a plurality of storage means to a lower temperature than that flowing to a less remote chamber.

2. The fluid refrigeration method which comprises supplying an initial quantity of refrigeration fluid at a given temperature and under high pressure along a path to an enclosed space, removing and storing heat from the fluid during supply along said path thereby initially cooling the fluid, continuing supply of high pressure fluid throughout said initial cooling thereby to maintain said high pressure by addition of fluid until a final quantity of cooled fluid under said high pressure is supplied to said space, discontinuing supply of high pressure fluid, eflecting expansion of said final quantity of fluid by delivery of energy external of said space thereby further to cool and extract energy from the fluid in said space, and exhausting the further cooled fluid from said space through said path, the further cooled fluid receiving heat previously stored along said path.

3. The fluid refrigeration method which comprises supplying an initial quantity of refrigeration fluid at a given temperature and under high pressure along a path to an enclosed space, removing and storing heat from the fluid during supply along said path thereby initially cooling the fluid, continuing supply of high pressure fluid throughout said initial cooling thereby to maintain said high pressure by addition of fluid until a final quantity of cooled fluid under said high pressure is supplied to said space, discontinuing supply of high pressure fluid, effecting expansion of said final quantity of fluid by delivery of mechanicalwork external of said space thereby further to cool and extract energy from the fluid in said space, and exhausting the further cooled fluid from said space through said path, the further cooled fluid receiving heat previously stored along said path.

4. The fluid refrigeration method which comprises supplying an initial quantity of refrigeration fluid at a given temperature and under high pressure along a path to an enclosed space, removing and storing heat from the fluid during supply along said path thereby initially cooling the fluid, continuing supply of high pressure fluid throughout said initial cooling thereby to maintain said high pressure by addition of fluid until a final quantity of cooled fluid under said high pressure is supplied to said space, discontinuing supply of high pressure fluid, effecting expansion of said final quantity of fluid by delivery of energy external of said space thereby further to cool and extract energy from the fluid in said space, and exhausting the further cooled fluid from said space through said path, the further cooled fluid delivering refrigeration to a thermal load in said path and then receiving heat previously stored along said path.

5. The fluid refrigeration method which comprises supplying an initial quantity of refrigeration fluid at a given temperature and under high pressure along a path to an enclosed space, removing and storing heat from the fluid during supply along said path thereby initially cooling the fluid, the heat being stored at continually lower temperatures along the path, continuing supply of high pressure fluid throughout said initial cooling thereby to maintain said high pressure by addition of fluid until a final quantity of cooled fluid under said high pressure is supplied to said space, discontinuing supply of high pressure fluid, effecting expansion of said final quantity of fluid by delivery of energy external of said space thereby further to cool and extract energy from the fluid in said space, and exhausting the further cooled fluid from said space through said path, the further cooled fluid receiving heat previously stored along said path.

6. Fluid expansion refrigeration apparatus comprising a fluid transfersystem including an enclosure, movable means forming With'the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chamber to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

7. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber through said conduit, said thermal storage means being adapted to progressively cool said fluid during admission therethrough, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chamber to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

8. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber through said conduit, said thermal storage means being adapted to progressively cool said fluid during admission therethrough, control means coordinating said movable means and valve means to supply an initial quantity of compressed fluid to said conduit and continue said supply while said movable means causes said chamber to expand, and take in a final quantity of cooled compressed gas, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

9. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chamber to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system, and means external of the system for absorbing said energy.

10. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chamber to expand, said con- '8 trolmeans being timed thereafter to cause said movable means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by motion of said movable means, and work absorbing means mechanically connected to said movable means for absorbing the energy of said motion.

11. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure a plurality of expansible chambers, and a conduit including thermal storage means connected to respective chambers; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from said chambers, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chambers to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chambers thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

12. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, a plurality of movable means forming with the enclosure a plurality of expansible chambers, and a conduit including a plurality of thermal storage means respectively connected to said chambers; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from said chambers, control means coordinating said movable means and valve means to supply a quantity of compressed lluid to said conduit while said movable means causes said chambers to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chambers thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

13. Fluid expansion refrigeration apparatus comprising a fluid transfer system including an enclosure, movable means forming with the enclosure a plurality of expansible chambers, and a conduit including thermal storage means connected to respective chambers; valve means connectcd to said conduit for admitting compressed fluid to and releasing fluid from said chambers, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit while said movable means causes said chambers to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chambers thereby to effect expansion and cooling of said quantity of fluid by delivcry of energy externally of said system, and means external of the system for absorbing said energy.

14. Fluid expansion apparatus in which a Working fluid is cooled comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber and heat exchange means between said thermal storage means and chamber; valve means comiected to said conduit for admitting compressed fluid to and releasing fluid from the chamber, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit While said movable means causes said chamber to expand, said control means being timed thereafter to cause one of said movable means and valve means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by delivery of energy externally of said system.

15. Fluid expansion apparatus in which a working fluid is cooled comprising a fluid transfer system including an enclosure, movable means forming with the enclosure an expansible chamber, and a conduit including thermal storage means connected to said chamber and heat exchange means between said thermal storage means and chamber; valve means connected to said conduit for admitting compressed fluid to and releasing fluid from the chamber, control means coordinating said movable means and valve means to supply a quantity of compressed fluid to said conduit While said movable means causes said chamber to expand, said control means being timed thereafter to cause said movable means to release pressure on the quantity of fluid in said chamber thereby to effect expansion and cooling of said quantity of fluid by motion of said 10 movable means, and work absorbing means mechanically connected to said movable means for absorbing the energy of said motion.

Bush May 9, 1939 Taeonis Sept. 11, 1951 

